Tries to load full page in the frame – all I want is the form to appear

I’m using the short code to insert a mixture of javascript and html in order for an email sign up form to work. It doesn’t load just the required piece, it appears to try to load an entire page!
[iframe src=”http://www.domain-name.com/page-name.php” width=”100%” height=”150″]

The page-name.php has been uploaded to the themes folder via FTP, as I was instructed. Can anyone help me with this? Thanks in advance.